Silicon single crystal pull-up apparatus

ABSTRACT

A silicon single crystal pull-up apparatus is used to pull up a doped silicon single crystal from a melt by means of the Czochralski process and includes a pull-up furnace, a sample chamber which is externally mounted on the pull-up furnace and houses a sublimable dopant, a shielding means for thermally isolating the interior of the pull-up furnace and the interior of the sample chamber, a sample tube which can be raised and lowered between the interior of the sample chamber and the interior of the pull-up furnace, and a raising and lowering means which is provided with guide rails on which the sample tube can slide and a wire mechanism by which the sample tube is raised and lowered along the guide rails.

TECHNICAL FIELD

The present invention relates to a silicon single crystal pull-upapparatus, more specifically to a silicon single crystal pull-upapparatus that retains a melt in a crucible in a pulling furnace andpulls a doped silicon single crystal from a melt by Czochralski (CZ)method.

BACKGROUND ART

Conventionally, as a method for adding a dopant to a silicon crystal, amethod of lowering a sample chamber housing a sublimable dopant down toa predetermined position above a melt in a pulling furnace, heating andsubliming a sublimable dopant by radiant heat from the melt, andintroducing the sublimable dopant, which is sublimed to the gaseousform, into the melt has been adopted.

As a method for introducing the dopant in the gaseous form to a melt, amethod in which an open end of a supply pipe is disposed above the meltand the dopant carried by a carrier gas composed of an inert gas such asargon gas is sprayed from the supply pipe toward the melt, can beexemplified.

According to the invention disclosed in Patent Document 1, a sample tube(doping tube) is disposed at a position that does not interfere with apulling mechanism and the sample tube is lowered down to just above anupper face of a crucible, thereby melting a dopant inside the sampletube by radiant heat from the melt at this position. Thereafter, thesample tube storing the dopant is lowered to a position so as to bedipped in the melt, thereby adding the melted dopant to the melt from anopen surface of the doping tube. A silicon single crystal ingot having adiscontinuous range of specific resistivities in a growing direction isthus pulled and grown.

[Patent Document 1] Japanese Unexamined Patent Application PublicationNo. 2005-336020

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

Patent Document 1 does not discuss in detail a method for moving asample tube up and down. For example, since the temperature inside apull-up apparatus is high, a sample tube may be supported and moved upand down by an elevation/descent means such as a heat-resistant arm.However, in a case of using an arm, there has been a problem in that adriving unit becomes bulky with increasing weight of the arm and a wholedevice for moving a sample tube up and down becomes bulky.

In addition, in a case where positioning or transfer of a sample tube isrequired, for example for connecting the sample tube to other supplymeans, the sample tube needs to be fixed at a predetermined angle ortransferred. However, in such a case, fine adjustment is difficult withan arm.

The present invention aims to provide a space-saving silicon singlecrystal pull-up apparatus provided with an elevation/descent means thatcan easily correct a position of a sample tube.

Means for Solving the Problems

In a first aspect of the present invention, a silicon single crystalpull-up apparatus that pulls a doped silicon single crystal from a meltby Czochralski method, includes: a pulling furnace; a sample chamberthat is externally attached to the pulling furnace and houses asublimable dopant; a shielding means that thermally shields an inside ofthe sample chamber from an inside of the pulling furnace; a sample tubethat can move up and down between the inside of the sample chamber andthe inside of the pulling furnace; and an elevation/descent meansprovided with a guide rail on which the sample tube can slide and a wiremechanism that moves the sample tube up and down along the guide rail.

According to a second aspect of the present invention, in the siliconsingle crystal pull-up apparatus as described in the first aspect, thewire mechanism is provided with a wire that is attached to the sampletube, a drum member that winds the wire, and a driving device thatdrives the drum member.

According to a third aspect of the present invention, in the siliconsingle crystal pull-up apparatus as described in the first or secondaspect, the guide rail is provided with a first guide rail that extendsfrom the inside of the sample chamber to the shielding means and asecond guide rail that extends from the shielding means to the inside ofthe pulling furnace, the first and second guide rails each have a groovethat fits an outer diameter of the sample tube, and the groove has, inan end portion of the first guide rail on a side to the shielding meansand in an end portion of the second guide rail on a side to theshielding means, a taper with an internal diameter that increasestowards the end portions.

According to a fourth aspect of the present invention, the siliconsingle crystal pull-up apparatus as described in any one of the first tothird aspects further includes a supply pipe inside the pulling furnace,which supplies the sublimable dopant discharged from the sample tube tothe melt, in which the supply pipe is provided with a joint portion thatis joined with the sample tube, and the sample tube, having sliddownward on the guide rail, is joined with the joint portion of thesupply pipe.

According to a fifth aspect of the present invention, the silicon singlecrystal pull-up apparatus as described in any one of the first to fourthaspects further includes a purge tube inside the pulling furnace foravoiding contamination of the melt with powder produced from sliding thesample tube on the guide rail.

According to a sixth aspect of the present invention, in the siliconsingle crystal pull-up apparatus as described in any one of the first tofifth aspects, the sublimable dopant is arsenic or red phosphorus.

EFFECTS OF THE INVENTION

According to the present invention, a space-saving silicon singlecrystal pull-up apparatus provided with an elevation/descent means thatcan easily correct a position of a sample tube can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing a silicon single crystal pull-upapparatus according to an embodiment of the present invention;

FIG. 2 is a schematic view of a cross-section showing anelevation/descent means according to the present embodiment;

FIG. 3 is a perspective view showing an arrangement of a doping tube anda guide rail according to the present embodiment; and

FIG. 4( a) is a schematic view of a cross-section in a state where thedoping tube according to the present embodiment is connected to a supplypipe and FIG. 4( b) is a partially enlarged view of FIG. 4( a).

PREFERRED MODE FOR CARRYING OUT THE INVENTION Pulling Furnace

An embodiment of a silicon single crystal pull-up apparatus 1 accordingto the present invention is described in detail hereinafter. FIG. 1 is aschematic view showing the silicon single crystal pull-up apparatus 1according to the present embodiment. FIG. 2 is a schematic view of across-section showing a positional relationship between a sample chamber20, a shielding means 24, a doping tube 21 as a sample tube, anelevation/descent means 25, and a supply pipe 22 according to thepresent embodiment. As shown in FIGS. 1 and 2, the silicon singlecrystal pull-up apparatus 1 of the present embodiment is provided with apulling furnace (chamber) 2 that can be used for crystal growth by CZmethod.

In the pulling furnace 2, a crucible 3 is provided for housing a melt 5that is obtained by melting a material consisting of polycrystallinesilicon (Si). The crucible 3 is composed of a graphite crucible 32 and aquartz crucible 31 thereinside. A heater 9 for heating and melting amaterial inside the crucible 3 is provided around the crucible 3.Between the heater 9 and an inner wall of the pulling furnace 2, a heatinsulation tube 13 is provided.

In addition, a pulling mechanism 4 is provided above the crucible 3. Thepulling mechanism 4 has a pulling cable 4 a and a seed crystal holder 4b that is attached to an end thereof. The seed crystal holder 4 b holdsa seed crystal.

In such a configuration, a material is put in the crucible 3 and heatedby the heater 9, thereby melting the material and obtaining the melt 5.When a melt state of the melt 5 is stabilized, the pulling cable 4 a islowered to dip a seed crystal (not shown) held by the seed crystalholder 4 b into the melt 5. After settling the seed crystal in the melt5, the pulling cable 4 a is pulled up in order to pulling and growingthe silicon single crystal (silicon ingot) 6 from the melt 5. Whilegrowing the silicon single crystal 6, the crucible 3 is rotated around arotational axis 10. Meanwhile, the pulling cable 4 a of the pullingmechanism 4 is rotated in the same direction as, or a differentdirection from, a rotational direction of the rotational axis 10. Here,the rotational axis 10 can be driven also in a perpendicular directionand can move the crucible 3 up and down to an arbitrary upper position.

At this time, the inside of the pulling furnace 2 is decompressed to avacuum state (for example, a few KPa) after shutting down outside air.In addition, argon gas 7 is supplied as inert gas to the inside of thepulling furnace 2 and discharged using a pump. By circulating argon gas7 inside the pulling furnace 2, vaporized material generated inside thepulling furnace 2 can be taken away to the outside of the pullingfurnace 2 along with argon gas 7. A feed rate of the argon gas 7 can beset for each of steps in the crystal growth.

As the silicon single crystal 6 grows, contact area between the melt 5and the crucible 3 changes due to a decrease in the amount of the melt5, and the amount of dissolution of oxygen from the crucible 3 changes.This affects a concentration distribution of oxygen in the siliconsingle crystal 6 that is to be pulled. Given this, a heat insulationplate 8 (gas flow tube) is provided above the crucible 3 and around thesilicon single crystal 6. The heat insulation plate 8 has a function ofguiding the argon gas 7 that is supplied from an upper side of thepulling furnace 2 to a center of a melt surface 5 a, and further to anouter peripheral portion of the melt surface 5 a via the melt surface 5a. As a result, the argon gas 7 is discharged from an outlet (not shown)provided in a lower side of the pulling furnace 2 along with a vaporizedmaterial from the melt 5. This can stabilize a gas flow rate on the meltsurface 5 a and maintain a constant rate of oxygen evaporation from themelt 5.

In addition, the heat insulation plate 8 has a function of insulatingthe seed crystal and the growing silicon single crystal 6 from radiantheat generated in a high-temperature part such as the crucible 3, themelt 5, the heater 9 and the like. Here, a distance between a lower endof the heat insulation plate 8 and the melt surface 5 a can be adjustedeither by up and down movement of the crucible 3 or by up and downmovement of the heat insulation plate 8 by an elevation device.

Sample Chamber

The sample chamber 20 contains a sublimable dopant 23 (impurity) thatdopes the silicon single crystal 6 to be grown. The sample chamber 20 isexternally attached to a flange portion of the pulling furnace 2 via ashielding means 24. Here, as the sublimable dopant 23 to be stored inthe sample chamber 20, N-type dopants for providing N-type electricalcharacteristics to the silicon single crystal 6, such as arsenic (As),red phosphorus (P) and antimony (Sb), can be exemplified. Particularly,arsenic (As) and red phosphorous (P) are sublimable dopants and can besublimed from a solid phase to a vapor phase at a relatively lowtemperature when used as the sublimable dopant 23.

When housing the sublimable dopant 23 in the sample chamber 20, it ispreferable that the sublimable dopant 23 is put into the doping tube 21as the sample tube and the doping tube 21 is housed in the samplechamber 20.

The doping tube 21 has a substantially cylindrical shape. The dopingtube 21 is disposed along a groove of a guide rail 25 b (a first guiderail 25 c and a second guide rail 25 d) provided to be extend from theinside of the sample chamber 20 to the inside of the pulling furnace 2.Then the doping tube 21 moves up and down from the inside of the samplechamber 20 to the inside of the pulling furnace 2 being guided by theguide rail 25 b. Specific shapes of the doping tube 21 and the guiderail 25 b are described later in detail.

By using the doping tube 21, the sublimable dopant 23 can be easilyloaded to and unloaded from the sample chamber 20. In addition, thesublimable dopant 23 can be infallibly supplied into the pulling furnace2 that is in operation. Here, a material that can resist hightemperatures due to the radiant heat of the melt, specificallytransparent quartz, can be used as a material for the doping tube 21.The doping tube 21 supplies the sublimable dopant 23 to the inside ofthe pulling furnace 2.

A vacuum pump (not shown) and an argon gas line (not shown) arepreferably provided to the sample chamber 20. By providing the vacuumpump and the argon gas line, pressure inside the sample chamber 20 isreduced or returned to ordinary pressure, independently from the pullingfurnace 2. As a result, a rapid change in pressure inside the samplechamber 20 can be reduced when a gate valve is opened or the doping tube21 is removed.

In addition, it is preferable to provide the sample chamber 20 with acooling mechanism. By providing the cooling mechanism, the doping tube21 heated in the pulling furnace 2 is efficiently cooled by combinationuse of the cooling mechanism and the argon gas. As a result, the dopingtube 21 can be exchanged more smoothly.

In addition to the shielding means 24, tubes with flanged ends can beinterposed between the sample chamber 20 and the pulling furnace 2. Inthis case, the tube can be provided with a cooling mechanism as with thesample chamber 20, or with a small window. Particularly, by providing atube with the small window, input of the sublimable dopant 23 can beeasily confirmed.

Shielding Means

The shielding means 24 thermally shields the sample chamber 20 from thepulling furnace 2. The shielding means 24 is provided between thepulling furnace 2 and the sample chamber 20. By providing the shieldingmeans 24, radiant heat and atmosphere of the inside of the pullingfurnace 2 is thermally blocked by the shielding means 24. As a result,the sublimable dopant 23 of a desired amount can be sublimed at adesired timing. For example, the shielding means 24 can be opened duringcrystal growth to supply the sublimable dopant 23 from the samplechamber 20.

A sliding gate valve can be preferably used as the shielding means 24.By using the sliding gate valve, a space of the shielding means 24 in astroke direction is reduced. Therefore, a transfer distance of thesublimable dopant 23 from the sample chamber 20 can be reduced. In thiscase, it is more preferable to use a cooling mechanism also in theshielding means 24. By using the cooling mechanism, the shielding means24 does not deteriorate by heat from the pulling furnace 2. Therefore,the sample chamber 20 can be infallibly thermally shielded from thepulling surface 2.

When the shielding means 24 is closed, radiant heat of the inside of thepulling furnace 2 does not reach the sublimable dopant 23 inside thesample furnace 20 and does not vaporize the sublimable dopant 23. As aresult, during a period after the beginning of growth of the siliconsingle crystal 6 and before first opening of the shielding means 24, thesilicon single crystal 6 being grown can be maintained additive-free,without the sublimable dopant 23.

Thereafter, the shielding means 24 is opened when doping of the siliconsingle crystal 6 with the sublimable dopant 23 is started, in otherwords when the shoulder portion and a first half of the straight bodyportion of the silicon single crystal 6 have grown. Here, when theshielding means 24 is being opened, the sublimable dopant 23 is storedat a predetermined position in the sample chamber 20, and a door of thesample chamber 20 is closed. Thereafter, the pressure inside the pullingfurnace 2 and the pressure inside the sample chamber 20 are adjusted byoperating a vacuum pump on the sample chamber 20 side, and the shieldingmeans 24 is opened. By opening the shielding means 24 to dope with theN-type sublimable dopant 23 in high concentration when a shoulderportion to a first half of the straight body portion of the siliconsingle crystal 6 is grown, a part from the shoulder portion to the firsthalf of the straight body portion is free of the sublimable dopant 23and a part from a second half of the straight body portion to a tailportion is doped with the sublimable dopant 23 in high concentration.Accordingly, the N++ type silicon single crystal 6 can be manufacturedthat has a resistivity of less than 0.01 Ωcm and N type electricalcharacteristics.

It should be noted that timing for beginning doping is not limited tothe abovementioned timing. For example, doping can be started beforepulling up the single crystal, in other words after a polycrystallinematerial inside the quartz crucible 31 is melted and before the seedcrystal is dipped into the melt 5.

When the N++ type silicon single crystal 6 of low resistivity is pulledand grown by adding the sublimable dopant 23 in high concentration,breakage of crystal is likely to occur. On the other hand, according tothe present embodiment, by using the shielding means 24, timing forsupplying the sublimable dopant 23, which provides N-type electricalcharacteristics to the silicon single crystal 6, can be preciselycontrolled. As a result, even if growth up to the first half of thestraight body portion of the silicon single crystal 6 takes an extendedamount of time, breakage of crystal can be alleviated.

The shielding means 24 can be closed not only after growth of thesilicon single crystal 6, but also during crystal growth, or aftersupplying the entire amount of the sublimable dopant 23. After closingthe shielding means 24, the pressure inside the sample chamber 20 isrestored to atmospheric pressure by introducing the argon gas 7 into thesample chamber 20, and then the sublimable dopant 23 can be repeatedlyinput by opening the door of the sample chamber 20.

Elevation/Descent Means

The elevation/descent means 25 moves the doping tube 21 up and down soas to connect the doping tube 21 with the supply pipe 22 (describedlater). The elevation/descent means 25 is provided with the guide rail25 b (the first guide rail 25 c and the second guide rail 25 d) on whichthe doping tube 21 can slide, and the wire mechanism 25 a that moves upand down the doping tube 21 along the guide rail 25 b.

The wire mechanism 25 a is provided with a wire 26 that is attached tothe doping tube 21, a winding drum 252 as a drum member, which winds thewire 26, and a motor 251 as a driving unit, which drives the windingdrum 252. The wire mechanism 25 a is a mechanism for moving the dopingtube 21 up and down along the guide rail 25 b with the wire 26. The wiremechanism 25 a drives the winding drum 252 by the motor 251 and adjustsa height of the doping tube 21 via the wire 26. Here, driving of themotor 251 by the wire mechanism 25 a is preferably controlled by aheight position of the doping tube 21 and an open/close state of theshielding means 24.

The wire 26 can be stored in the winding drum 252. The wire 26 isrequired to have such a length that the doping tube 21 can move up anddown from an end portion of the sample chamber 20 on a side to the wiremechanism 25 a to the inside of the pulling furnace 2, and the length ofthe wire 26 is not particularly limited. The wire 26 is composed ofheat-resistant metal such as molybdenum. The wire 26 is configured to beengaged with and fixed on an end portion in a longitudinal direction ofthe doping tube 21.

The guide rail 25 b is provided with the first guide rail 25 c thatextends from the inside of the sample chamber 20 to the shielding means24 and the second guide rail 25 d that extends from the shielding means24 to the inside of the pulling furnace 2. The first guide rail 25 c andthe second guide rail 25 d are provided between the inside of the samplechamber 20 and the supply pipe 22, and define a position at which thedoping tube 21 moves up and down. By providing the first guide rail 25 cand the second guide rail 25 d, the doping tube 21 can be connected tothe supply pipe 22 more firmly, and the sublimable dopant 23 can betransferred to the supply pipe 22 more infallibly. The guide rail 25 bis preferably composed of a graphite material. By using a graphitematerial, the guide rail 25 b can be highly heat-resistant andrestriction of a shape thereof can be reduced.

As shown in FIG. 1, the elevation/descent means 25 is disposed at aposition that does not interfere with the silicon single crystal 6 andthe pulling mechanism 4 and does not dip into the melt 5. By disposingthe elevation/descent means 25 at a position that does not interferewith the pulling mechanism 4, the sublimable dopant 23 can be inputwhile pulling the silicon single crystal 6.

The shielding means 24 is provided to be orthogonal to a direction inwhich the first guide rail 25 c and the second guide rail 25 d extendfrom the inside of the sample chamber 20 to the inside of the pullingfurnace 2. As shown in FIG. 3, a groove 253 that fits an outer diameterof the doping tube 21 is formed on each of the first guide rail 25 c andthe second guide rail 25 d. FIG. 3 is a perspective view showing anarrangement of the doping tube 21 and the guide rail 25 b. For the sakeof convenience of description, the shielding means 24 between the firstguide rail 25 c and the second guide rail 25 d is omitted. The groove253 has a shape of a longitudinally-halved cylinder, with asubstantially semicircular vertical cross-section. The groove 253 has aninternal diameter that is slightly larger than the outer diameter of thedoping tube 21, so that the doping tube 21 can slide.

In an end portion of the first guide rail 25 c on a side to theshielding means 24 and in an end portion of the second guide rail 25 don a side to the shielding means 24, tapers 254 a and 254 b are formedeach having an internal diameter that increases towards the end portion.

In a state where the shielding means 24 is open, a gap of a size of theshielding means 24 is formed between the first guide rail 25 c and thesecond guide rail 25 d. However, in the end portions of the first guiderail 25 c and the second guide rail 25 d on the side to the shieldingmeans 24, the tapers 254 a and 254 b are formed each having an internaldiameter that increases towards the end portion. As a result, even ifthe doping tube 21 is tilted while passing through the gap between thefirst guide rail 25 c and the second guide rail 25 d in a state wherethe shielding means 24 is open, the tilt of the doping tube 21 iscorrected by the tapers 254 a and 254 b. Accordingly, the doping tube 21is smoothly transferred between the first guide rail 25 c and the secondguide rail 25 d, and can move up and down smoothly on the guide rail 25b.

Doping Tube

As shown in FIG. 3, the doping tube 21 is provided with a main body 214that is tubular and, on a first end portion in a longitudinal directionof the doping tube 21, a convex portion 211 that projects in thelongitudinal direction. The first end portion in a longitudinaldirection of the doping tube 21 is an end portion of the doping tube 21directed toward the inside of the pulling furnace 2 in a state where thedoping tube 21 is disposed on the guide rail 25 b (hereinafter referredto as a “lower end portion”). The convex portion 211 projects from asubstantially central portion of an end surface 215 of the main body 214of the doping tube 21 and has a substantially spherical shape. Thephrase “substantially spherical shape” indicates a shape that is not aperfect sphere but a large portion thereof has a spherical curvedsurface.

As shown in FIG. 4, the convex portion 211 is hollow. FIG. 4( a) is aschematic view of a cross-section in a state where the doping tube 21 isconnected to the supply pipe 22. FIG. 4( b) is a partially enlarged viewof FIG. 4( a). The doping tube 21 is provided with a through hole 212that communicatively connects the inside of the doping tube 21 to theoutside, on a lowermost portion thereof in a longitudinal direction. Tothe through hole 212, a plate 216, on which a plurality of holes thatare smaller than the through hole 212 are formed, is attached. Adiameter of each hole of the plurality of holes is approximately 2 mm.In such a configuration, the sublimable dopant 23 stored inside thedoping tube 21 can be prevented from falling out from the through hole212. When the shielding means 24 opens, the doping tube 21 slides downthe guide rail 25 b by a drive of the wire mechanism 25 a. As shown inFIGS. 4( a) and 4(b), after sliding down, the doping tube 21 is joinedwith the supply pipe 22 provided inside the pulling furnace 2. When thedoping tube 21 is joined with the supply pipe 22, a flow path connectingthe inside of the doping tube 21 to the inside of the supply pipe 22 isformed from a hole on the plate 216 attached to the through hole 212.

In addition, the doping tube 21 is provided with a projection 213 thatprojects downwards in the longitudinal direction of the doping tube 21,from the end surface 215 of the main body 214. An outer surface of theprojection 213 is inclined from an outer periphery side of the dopingtube 21 toward the convex portion 211. A height of the projection 213 (aheight from the end surface 215 in the longitudinal direction of thedoping tube 21) is less than a height of the convex portion 211 (aheight from the end surface 215 in the longitudinal direction of thedoping tube 21). Even if the doping tube 21 is tilted while passingthrough the gap between the first guide rail 25 c and the second guiderail 25 d in a state where the shielding means 24 is open, the tilt ofthe projection 213 is corrected by the tapers 254 a and 254 b.Accordingly, the doping tube 21 is smoothly transferred between thefirst guide rail 25 c and the second guide rail 25 d, and can move upand down smoothly on the guide rail 25 b.

It should be noted that, on a second end portion of the doping tube 21,an opening for loading and unloading the sublimable dopant 23 and a cap217 for sealing the opening are provided. On the doping tube 21, theprojection 213 is also provided in the second end portion as in thefirst end portion, for moving up and down on the guide rail 25 b.Accordingly, when the doping tube 21 is pulled up by the wire mechanism25 a, the doping tube 21 can move up and down smoothly between the firstguide rail 25 c and the second guide rail 25 d.

Supply Pipe

As shown in FIG. 4( a), the supply pipe 22 is joined with the dopingtube 21 having descended by the elevation/descent means 25. The supplypipe 22 guides the sublimable dopant 23, which has vaporized by radiantheat from the melt 5 and the like, to the melt 5. The supply pipe 22supplies the sublimable dopant 23 ejected from the doping tube 21 to theinside of the pulling furnace 2.

As shown in FIG. 1, the supply pipe 22 is disposed at a position thatdoes not interfere with the silicon single crystal 6 and the pullingmechanism 4 and does not dip into the melt 5. As described later, on afirst end of the supply pipe 22, a joint portion 222 that is joined withthe convex portion 211 of the doping tube 21 is provided. Any materialthat can resist high temperatures due to radiant heat from the melt andthe like, specifically quartz, can be used as a material for the supplypipe 22.

The supply pipe 22 is disposed at a position that does not interferewith the pulling mechanism 4. In such an arrangement, the sublimabledopant 23 that has vaporized can be guided to the melt 5 while pullingthe silicon single crystal 6, thereby allowing highly accurate dopingduring pulling of the crystal. In addition, by disposing the supply pipe22 at a position so as not to dip into the melt 5 and spraying thesublimable dopant 23 that has vaporized from the supply pipe 22 onto themelt 5, vibration, decrease in temperature, and change in convection ofthe melt 5 due to dipping of the supply pipe 22, the sublimable dopant23 and the like into the melt 5 can be alleviated. In addition, bystabilizing a crystallization ratio of a single crystal that is beinggrown, an adverse effect on a crystal state of the silicon singlecrystal 6 that is grown can be reduced. Here, the supply pipe 22 ispreferably disposed at such a position that input efficiency of thesublimable dopant 23 into the melt 5 is maximized when the sublimabledopant 23 is sprayed onto the melt 5.

As shown in FIG. 4( a), the supply pipe 22 is provided with a main body224 that guides the sublimable dopant to the melt 5 and the jointportion 222 provided on a first end portion in a longitudinal directionof the supply pipe 22 that projects in the longitudinal direction. Thefirst end portion is an end portion of the supply pipe 22 directedtoward the second guide rail 25 d in a state where the supply pipe 22 isdisposed inside the pulling furnace 2 (hereinafter referred to as an“upper end portion”). As shown in FIG. 4( b), the joint portion 222includes a concave portion 221 that has a concave shape into which theconvex portion 211 of the doping tube 21 can fit. The convex portion 211of the doping tube 21 and the concave portion 221 of the supply pipe 22compose a ball joint structure as a joint means for joining the dopingtube 21 with the supply pipe 22. The concave portion 221 is disposed ona track of the first guide rail 25 c and the second guide rail 25 d soas to fit onto and to be joined with the convex portion 211 of thedoping tube 21 that has slid down the second guide rail 25 d.

An inner surface of the concave portion 221 is a contacting surface withthe convex portion 211 of the doping tube 21. The contacting surface isformed to be a curved surface. The inner face of the concave portion 221has a curved shape corresponding to an outer face of the convex portion211 of the doping tube 21. A hole 223 is formed in the deepest part ofthe concave portion 221, the hole 223 being connected to the supply pipe22 that is hollow. When the doping tube 21 is joined with the supplypipe 22, a flow path connecting the inside of the doping tube 21 to theinside of the supply pipe 22 is formed, thereby guiding the vaporizedsublimable dopant to the melt 5.

Purge Tube

As shown in FIG. 1, a purge tube 14 is provided from an upper side to alower side in the pulling furnace 2. The purge tube 14 extends downwardsfrom the upper side of the pulling furnace 2, and further extends fromthe joint portion of the supply pipe 22 to an upper surface of the melt5 along the supply pipe 22. The purge tube 14 prevents carbon powder,which is powder generated from the guide rail 25 b due to friction whenthe doping tube 21 moves up and down along the guide rail 25 b, fromcontaminating the melt 5.

Next, an example of an in use state of the silicon single crystalpull-up apparatus 1 according to the present embodiment is describedwith reference to FIGS. 2 to 4. The sublimable dopant 23 is suppliedinto the doping tube 21. During input of the sublimable dopant 23, theshielding means 24 is closed and pressure inside the sample chamber 20is equal to atmospheric pressure. After input of the sublimable dopant23 into the doping tube 21, the pressure inside the sample chamber 20 isadjusted to predetermined pressure and the shielding means 24 is opened.

The doping tube 21 is connected to the wire 26 of the wire mechanism 25a. A motor 251 of the wire mechanism 25 a drives the winding drum 252and reels out the wire 26. As a result, the doping tube 21 connected tothe wire 26 descends. When the shielding means 24 is open, the dopingtube 21 descends along the first guide rail 25 c and the second guiderail 25 d.

In a state where the shielding means 24 is open, a gap is formed betweenthe first guide rail 25 c and the second guide rail 25 d. However, in anend portion of the first guide rail 25 c on a side to the shieldingmeans 24 and in an end portion of the second guide rail 25 d on a sideto the shielding means 24, tapers 254 a and 254 b are formed each havingan internal diameter that increases towards the end portion. As aresult, even if the doping tube 21 is tilted while passing through thegap between the first guide rail 25 c and the second guide rail 25 d ina state where the shielding means 24 is open, the tilt of the dopingtube 21 is corrected by the tapers 254 a and 254 b. Accordingly, thedoping tube 21 is smoothly transferred between the first guide rail 25 cand the second guide rail 25 d, and can move up and down smoothly on theguide rail 25 b.

In addition, the projection 213 that is inclined from the outside towardthe inside of the doping tube 21 is provided in an end portion in alongitudinal direction of the doping tube 21, thus the doping tube 21can move up and down more smoothly.

The doping tube 21 descends along the groove 253 formed on the guiderail 25 b. The doping tube 21 is supported by the wire 26 and passesthrough an end portion of the second guide rail 25 d on a side to thepulling furnace 2. The doping tube 21 having descended on the guide rail25 b is connected to the joint portion 222 of the supply pipe 22 that isdisposed on an extended line of the groove 253. The convex portion 211provided in a lower end portion of the doping tube 21 is guided by theguide rail 25 b and engaged with the concave portion 221 provided in anupper end portion of the supply pipe 22.

In a lowermost portion of the convex portion 211, the through hole 212is provided. To the through hole 212, the plate 216 having the pluralityof holes is attached. On the other hand, the deepest part of the concaveportion 221 is the hole 223, which is connected to the inside of thesupply pipe 22. Accordingly, a flow path is formed between the dopingtube 21 and the supply pipe 22 when the convex portion 211 is engagedwith the concave portion 221. The vaporized sublimable dopant 23 insidethe doping tube 21 flows into the supply pipe 22 via the flow path andis sprayed onto an upper surface of the melt 5 below the supply pipe 22.

In this case, since the convex portion 211 and the concave portion 221as the joint means are in a ball joint structure, even if there is aslight misalignment in the angle at which the doping tube 21 isconnected to the supply pipe 22, the angle can be changed in a state inwhich the convex portion 211 is engaged with the concave portion 221. Inaddition, since the guide rail 25 b is provided in an inclined statetoward the inside of the pulling furnace 2 and the weight of the dopingtube 21 having slid on the inclined guide rail 25 b is applied to theconvex portion 211, the convex portion 211 and the concave portion 221contact each other more tightly.

The silicon single crystal pull-up apparatus of the present embodimentprovides the following effects. Since the doping tube 21 is moved up anddown by the wire mechanism 25 a in the present embodiment, anelevation/descent means for moving the doping tube 21 up and down can bereduced in size and weight compared to a case of using an arm and thelike. In addition, the elevation/descent means having a simpleconfiguration can be easily maintained, repaired and the like.Furthermore, since the doping tube 21 moves up and down in a state ofbeing guided by the guide rail 25 b, by adjusting an angle and positionof the guide rail 25 b when connecting the doping tube 21 to the supplypipe 22, an angle and position of the doping tube 21 can be finelyadjusted.

In the present embodiment, in the end portions of the first guide rail25 c and the second guide rail 25 d on the side to the shielding means24, the tapers 254 a and 254 b are formed each having an internaldiameter that increases towards the end portion. As a result, even ifthe doping tube 21 is tilted while passing through the gap between thefirst guide rail 25 c and the second guide rail 25 d in a state wherethe shielding means 24 is open, the tilt of the doping tube 21 iscorrected by the tapers 254 a and 254 b. Accordingly, the doping tube 21is smoothly transferred between the first guide rail 25 c and the secondguide rail 25 d, and can move up and down smoothly on the guide rail 25b.

In the present embodiment, the purge tube 14 is disposed inside thepulling furnace 2. Since the guide rail 25 b is composed of a graphitematerial, carbon powder is generated when the doping tube 21 slides onthe guide rail 25 b. By providing the purge tube 14, the carbon powdercan be prevented from contaminating the melt 5.

It should be noted that an embodiment of the present invention and atechnical scope of the present invention are not limited to the abovedescribed embodiments.

For example, although the sublimable dopant 23 is supplied to the melt 5by a spraying method in the embodiment, the present invention is notlimited thereto and a dipping method that dips the supply pipe 22 intothe melt 5 can also be used for supplying the sublimable dopant 23 tothe melt 5.

In addition, a carrier gas introduction pipe (not shown) can also beused. The carrier gas introduction pipe is to be communicativelyconnected to the doping tube 21. The carrier gas introduction pipe is tointroduce carrier gas that is supplied from a gas supply source (notshown) for transferring a dopant into the doping tube 21. By introducingthe carrier gas, the sublimable dopant 23 that has vaporized can beefficiently guided to the melt 5 via the supply pipe 22 withoutretention in the doping tube 21. The carrier gas introduction pipe iscomposed of, for example, quartz. Inert gas such as argon gas is used asthe carrier gas.

1. A silicon single crystal pull-up apparatus that pulls a doped siliconsingle crystal from a melt by Czochralski method, the apparatuscomprising: a pulling furnace; a sample chamber that is externallyattached to the pulling furnace and houses a sublimable dopant; ashielding means that thermally shields an inside of the sample chamberfrom an inside of the pulling furnace; a sample tube that can move upand down between the inside of the sample chamber and the inside of thepulling furnace; and an elevation/descent means provided with a guiderail on which the sample tube can slide and a wire mechanism that movesthe sample tube up and down along the guide rail.
 2. The silicon singlecrystal pull-up apparatus according to claim 1, wherein the wiremechanism is provided with a wire that is attached to the sample tube, adrum member that winds the wire, and a driving device that drives thedrum member.
 3. The silicon single crystal pull-up apparatus accordingto claim 1, wherein the guide rail is provided with a first guide railthat extends from the inside of the sample chamber to the shieldingmeans and a second guide rail that extends from the shielding means tothe inside of the pulling furnace, the first and second guide rails eachhave a groove that fits an outer diameter of the sample tube, and thegroove has, in an end portion of the first guide rail on a side to theshielding means and in an end portion of the second guide rail on a sideto the shielding means, a taper with an internal diameter that increasestowards the end portions.
 4. The silicon single crystal pull-upapparatus according to claim 1, further comprising a supply pipe insidethe pulling furnace, which supplies the sublimable dopant dischargedfrom the sample tube to the melt, wherein the supply pipe is providedwith a joint portion that is joined with the sample tube, and the sampletube, having slid downward on the guide rail, is joined with the jointportion of the supply pipe.
 5. The silicon single crystal pull-upapparatus according to claim 1, further comprising a purge tube insidethe pulling furnace for avoiding contamination of the melt with powderproduced from sliding the sample tube on the guide rail.
 6. The siliconsingle crystal pull-up apparatus according to claim 1, wherein thesublimable dopant is arsenic or red phosphorus.